The present invention relates to scoring of sheet metal to form a weakening line capable of being severed by a minimum force.
Weakening lines are used in containers for defining a removable panel section in the panel of the end closure. These weakening lines are generally formed by scoring in a manner such that the sheet metal is crushed to a predetermined thickness. The crushed thickness remaining is generally designated as the residual. In easy opening container structures it is essential that the residual is maintained at a minimum to facilitate the manual opening of the container. At the same time the residual must be sufficiently strong so as to resist fracture during normal handling so that the container remains tightly sealed until opening.
These conditions have been difficult to achieve and in particular when the end closure is made from a relative non-ductile material such as steel. Although it should be understood that care must also be taken to prevent inadvertent fracture when the material is aluminum.
The fracture during normal handling is believed to be caused by work hardening stresses or the like created during the scoring. Heretofore, it has been common practice to provide an additional score of lesser residual than the primary score. These lesser residual scores are known as anti-fracture scores and are not intended to provide a weakening line along which the end unit panel is to be severed. The anti-fracture scores have been concentrically located in radially spaced relation to the primary score line.
The radial spacing of the anti-fracture score from the primary score or weakening is not always convenient and frequently interferes with other structures which may be incorporated into the end unit.
By the present invention there is provided a primary score incorporating an anti-fracture means which is not located in radial spaced relation to the primary score. This is accomplished by a single score having a cross-section including a pair of inclined walls merging toward a scoring face which is spaced from one surface of the panel to provide a residual capable of being severed. At least one of the inclined walls has two offset sections connected by a land or ledge which is vertically spaced from the scoring face.
The above described score cross-section is accomplished by a scoring tool shaped generally complementary to the score.